1. KEY CONCEPT Genes encode proteins that produce a diverse range of traits.

2. The same gene can have many versions.
A gene is a piece of DNA that directs a cell to make a certain protein.
Each gene has a locus, a specific position, on a pair of homologous chromosomes.
Different versions of the same gene are called alleles

3. An allele is any alternative form of a gene occurring at a specific locus on a chromosome.
Each parent donates one allele for every gene.
Homozygous describes two alleles that are the same at a specific locus.
Heterozygous describes two alleles that are different at a specific locus.

4. Genes influence the development of traits.
The genome is the collection of all of an organism’s genetic material.
All of the genes on all of the chromosomes.
A genotype refers to the makeup of a specific set of genes.
the alleles of a specific gene
Bb, BB, bb, where B=brown eyes, b=blue eyes
A phenotype is the physical expression of a trait.
Blue eyes or brown eyes

5. Alleles can be represented using letters.
A dominant allele is expressed as the phenotype when at least one allele is dominant.
A recessive allele is expressed as the phenotype only when two copies are present.
Dominant alleles are represented by UPPERCASE letters; recessive alleles by lowercase letters. r R Rr r r rr

6. Both homozygous dominant and heterozygous genotypes yield a dominant phenotype.
Most traits occur in a range and do not follow simple dominant-recessive pattern.
Height is a good example.

7. Ernest Hemingway had a bunch of cats when he lived in Key West, Florida
When he died he left the house to his cats
Some of these cats had an extra toe (called polydactyly)
Polydactyly is a dominant trait, so now all the cats there have extra toes.
There is no real advantage to extra toes. It just happens to be dominant over the other alleles so it is passed on.